refactor(logging): reduce download log spam and set INFO level

- Pass app logger to yt-dlp so internal [download] progress lines
  are routed through the INFO-level logger instead of stdout.
- Throttle download_progress_handler debug logging to avoid
  flooding logs on every fragment tick.
- Switch key provider lifecycle messages to INFO (start/complete)
  while keeping verbose details at DEBUG.
- Set debug_enabled=False in development config so dev mode
  does not emit extra debug noise.
- Update config docstring example from DEBUG to INFO.

src/core/SeriesApp.py

@@ -445,9 +445,12 @@ class SeriesApp:
         try:
             def download_progress_handler(progress_info):
                 """Handle download progress events from loader."""
-                logger.debug(
-                    "download_progress_handler called with: %s", progress_info
-                )
+                # Throttle progress logging to avoid spam
+                status = progress_info.get("status", "")
+                if status in ("downloading", "finished"):
+                    logger.debug(
+                        "download_progress_handler called with: %s", progress_info
+                    )
 
                 downloaded = progress_info.get('downloaded_bytes', 0)
                 total_bytes = (